Nylon carpeting (i.e., carpeting having nylon-6 and/or nylon-6,6 fibers tufted into a non-nylon backing material) is an extremely popular flooring material for residential and commercial buildings. Although quite durable, nylon carpeting does have a finite useful life and therefore must be replaced at periodic intervals in order to maintain the interior aesthetics of the residential or commercial building in which it is installed. Once the used carpeting has been removed, it has typically been discarded as post-consumer landfill waste. Needless to say, reducing (or eliminating) the vast amount of post-consumer carpeting that is discarded annually as landfill waste is quite attractive to both the landfill operators (since the strain on landfill capacity can be reduced) and nylon processors (since waste carpeting represents a potentially large source of low-cost nylon raw material).
Recycling of nylon carpeting, however, is problematic since its three basic components--i.e., nylon carpet fibers, at least one backing material formed typically from polyolefins, such as polypropylene, and an adhesive material of styrene-butadiene rubber (SBR) applied as a latex and typically filled with an inorganic filler such as calcium carbonate--are chemically and physically diverse. Thus, in order to be economically viable, the art has typically sought ways in which these three basic carpeting components could be separated and isolated from one another so that the commercially valuable nylon carpet fibers can be recycled.
As examples of prior art techniques that have been proposed to reclaim carpeting, the reader's attention is directed to the following U.S. Patents (the entire content of each being incorporated expressly hereinto by reference) which are believed to be representative of this art area:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 5,230,473 Hagguist et al Jul. 27, 1993 5,233,021 Sikorski Aug. 3, 1993 5,294,384 David et al Mar. 15, 1994 5,169,870 Corbin et al Dec. 8, 1992 ______________________________________
The Hagguist et al '473 patent describes a carpet reclamation system whereby the waste carpeting is subjected to a series of mechanical, hydraulic, fluid, heat and pressure devices so as to separate the carpeting into its basic components which are individually collected.
Polymeric materials are extracted from a multi-component product, such as carpeting, by subjecting the multi-component product to a multi-stage extraction process according to the Sikorski '021 patent. Specifically, according to the Sikorski '021 patent, since each polymer material component of the mixture has a different range of temperatures and pressures at which it is soluble in a given supercritical fluid, the material may be treated by adjusting the temperature and pressure of a suitable fluid so that the fluid becomes supercritical in order to solubilize that component in the mixture having the lowest range of solubility temperatures and pressures. By removing the polymer-containing solution and again treating the remaining components of the mixture in a suitable fluid and under suitable pressure/temperature conditions, the remaining components may be removed and separated in a step-wise manner.
The technique proposed by the David et al '384 patent does not attempt to separate the waste carpeting components. Instead, the David et al '384 patent suggests that the entirety of the waste carpeting may be formed into a melt blend under conditions of temperature, pressure and intensive mixing sufficient to produce a heterogeneous composition which exhibits thermoplastic properties which is said to be useful "as is" in a variety of applications.
The Corbin et al '870 patent discloses a process whereby .epsilon.-caprolactam may be reclaimed from nylon-6 carpet waste. Specifically, according to the Corbin et al '870 patent, it is not essential that most of the polypropylene, latex and other non-nylon carpeting components be separated from the nylon component. Thus, the process of Corbin et al '870 is capable of tolerating the presence of non-nylon carpeting components such as the polypropylene backing, calcium carbonate-containing latex and the like, while still producing .epsilon.-caprolactam which contains only those impurities derived from the nylon-6 component.